Corrosion recorder



April 1945- M. G. FONTANA ET AL 5 2,374,088

GORROISION RECORDER Filed an. 28, 1941 .Marselz'o GFozaZana' Gordon W Kidder v Ph'z'Z'z 'o B;.I4/'21az2s INVENTORS ATTORNEY 'tential between the electrodes fllmon the metal or alloy. completely removed by clinical action, the metal or alloy becomes blah-- rapid deterioration. 1i permitted to reiorm within riqd oralloy will continue-to u Patented Apr. 17, 1945 UNITED, s'rATEs :IP'ATENT OFFICE coaaosrou nacoam-za W.- Kidder, Bridgeport, Comm, and Philip B. Kraus, Roselle Park, N. .L, assignors to E. I. du

Pont' de Nemours 8; Company, DeL, a corporation of Delaware Wilmington,

Application January 28, 1941, Serial No. svazaa fcorrode or dissolve. The continued presence of This invention relates to apparatus for recording the corrosive nature of. various media, and

more particularly todevices'for automatically de-' trminingand controlling theeorrosiveness (incipient or advanced) 'of solutions or slurries which come in contact with metallic equipment, ele- :ments or parts employed in various commercial operations; By the term .incipientlcorrosion," we intend to include that degree or corrosion which takes placeprior to anyappreciable deterioration or al or element. I

When electrodes composedof'dissimilar-metals are suitably immersed or otherwise disposed in separated relationship in a contacting corrosive solution, a difier'enceof' electrical potential is set up therebetween. when the corrosive con-. dition of thesolution towards a particular metal 10 actual corrosionof arrinvolved metor alloy increases, a rise in-the difference of pooften results. Conversely, when the, corrosiveness decreases or weakens, a reduction-in the electrical potential often takes place. For instance, if two'e'lectrodes composed of dissimilar metals are immersed in an acidic or like corrosive solutionanda circuit is formed by-connectingthem together voltage .applied-atits terminals, the interpositioningin the circuit or a sensitive instrument, such as a potentiometenwill directly indicate the elec-' trical potential which exists between said elecby means. of an electrical conductor, such as copper wire, a current will flow,

i may "ensue.

the abnormally corrosive. solution will therefore hinder or'entirely prevent the reformation oi the protective film. I

Thecontinued, uninterrupted presence of a protective film onthe metal may also prove disadvantageous because 01' its tendency to act as an insulator to preventthe immediate detection and correction of an undesired change in the corrosive characteristics of a liquid, either to the incipient or advanced stage. Thus, if the media the corrosive nature of which is being ascertained is not originally. corrosive towards a particular metal, a

protective film will build up on the electrodes and a subsequent change in the corrosive nature of the solution will not be detected until the protective film is completely removed from the electrodes-and thelatter then replaced in the solution. In theinterim, it an abnormal corrosion condition actually exists, irreparable damage It-is accordingly among the objects of this invention to provide novel means for overcomingthe above as well as other difliculties which have been heretofore encountered incorrosion recording devices. A further and particular object is to provide useful means for-immediately, accurately and practically ascertaining when a noncorrosive solution changes to one which is corrosive in character. A still further object is'to provide novel means for ascertaining the film formtrodes. Since the diiierence elf-electrical potential between two electrodes is oitena function of the corrosiveness'oi" the solution and a definite relationship appears to exist between the currentand-the rate atewhich the electrodes corrode or deteriorate, the corrosive nature ofany solution i may be readily ascertained by measuring this dif-' ierence in electrical potential between electrodes.-

The resistance which a contacting metal or alloy, suchas'stainless steel, exhibits towards corrosive media largelydepends on the ability or such media to form an adherent surface or protective If this him should be either chemical or meing ability or capacity of a solution on metal or alloy ,electrodes. An additional object is to provide means for actuating a corrective control mechanism or signalling device when a given solution'iails to replace a protective film on a metal electrode. An additional object is to provide a novel combination of elements adapted to automatically control the qualitative nature of a, given solution, as well as automatically correct and remedy incipient or advanced corrosiveness upon its, occurrence. *Otherobjects of the invention will be apparent from the ensuing description and accompanying diagrammatic drawing.

The above mentioned as well as other objects and advantages are attainable in our invention which. comprises electrically indicating and/or -and will thereupon become highly susceptible to this protective fllm' isnot .a relatively short pecontrolling or regulating the corrosive or how corrosive characteristics of a solution by providing, in combination, connected electrodes or ter minals .in contact with said solution, electrically sensitive means responsive to a diiierence'in electrical potential in the circuit, arranged, in series with said electrodes and solution, and additional,

means for periodically removing any protective film formed on said electrodes.

In a more specific and preferred embodiment of our invention, a novel apparatus for indicating the film-forming ability of solutions or slurries on metals or alloys is provided, which comprises, in combination, an electrical circuit, including a pair of electrodes of dissimilar metals or alloys connected together by an electrical conductor, said electrodes being in contact with or immersed in a solution or slurry to be tested, a recorder potentiometer interpositioned in said circuit responsive to the current flowing therein, a battery or other source of electrical current in said circuit adapted to periodically impress a counter E. M. F. in said circuit and remove any protective surface film formed on said electrodes, and a signalling and/or corrective-control means actuated by said potentiometer for indicating and/or correcting the failure of the solution or slurry to reform said protective film on said electrodes after each periodic removal.

The invention will be more readily understood when considered in connection with the ensuing description and accompanying drawing. the latter diagrammatically illustrating one preferred adaptation thereof and wherein a solution or slurry to be tested is continuously supplied to and withdrawn from a suitable vessel or container.

For purposes of illustration, the invention will be described as applied, for instance, to themetection of, a delicate, stainless steel type oi screening apparatus (not shown) and such as is employed in centrifugal or other types of apparatus. Such screening element may be provided, for instance, with a plurality of small openings or apertures of, say, about .01" in diameter and during use is in continuous contact with a'solution such as hydrogen sulfide which is not normally corrosive to the particular alloyof which said screen element is made up. Under certain conditions of operation, however, especially when the sulfide content of such solution increases due to a desired or unavoidable change in the operating procedure, the solution may become more or less corrosive to said screen and thereupon deleteriously attack and damage the metal. Un-

less this corrosive condition is remedied withinv a relatively short period of time, such as by substantially immediate neutralization after reaching acorrosivestate, the openings in the screen element will become unduly enlarged and seriously damaged, due to corrosion attack, to ultimately render the screen wholly unfit and entirely ineffective for its intended use and purtainer I is shown, provided with a suitable inlet l I and outlet l2, and adapted to retain a suitable solution l3 which may be eithercorrosive or noncorrosive in nature, e. g., acid, alkaline, or neutral. If-desired, the container It may conveniently comprise an enlarged conduit or section of pipe in the main flow, or, alternatively, may comprise auxiliary equipment associated in a bypass line which may be in either valved or open communication with said main flow. Suitably positioned for contactin the solution 13 and in substantially spaced relationship from each other, but-out of contact with the container l0, two electrodes H and I! are provided, constructed, preferably, of dissimilar metals or alloys. One such electrode consists preferably of substantially the same type of metal or alloy 'gree. tration, said other electrode may conveniently be constructed of a stainless steel known in the inaccurate potential readings.

which are to be protected should be'constructed of an alloy composed of, say, 18% chromium, 8% nickel, .0'l'% carbon, and the remainder substantially all iron, one of the aforesaid electrodes is preferably constructed of this same composition. The other electrode may conveniently be constructed of a stainlesssteel type of composition known topossess positive resistance to the solution under test, if and when the same should become corrosive in character and to any given de- For example, in the instance under illustrade as Carpenter No. 3 containing about 20% ch'romium, 1% copper,.25% carbon, and the balance substantially all iron.

The electrodes i4 and 15 may be suitably supported in the solution I3 in any desired manner and by any desired and convenient means. Suitably disposed on said electrodes are rubber covering elements 16, adapted to protect them at the liquid-air line, this being essential to prevent excessive rates of corrosion of the metal, and also Suitably connected to said electrodes, electrical conducting wires i1 and 48 are provided, which lead and are connected to a recording potentiometer or equivalent voltage measuring device 20,0: any well known operable electrical make through a relay 2|, whereby the potential difierence between the electrodes will be recorded on said potentiometer.

The solution to be tested completes the electrical circuit.

In order to maintain the electrodes at maxi- 40 mum sensitivity at all times, periodically we remove any protective film formed on said electrodes, thereby permitting one to determine whether the protective film can or cannot be reformed by the solution in question. In the present embodiment of the invention, this may be accomplished by providing in the circuit a suitable source of electric current 22, .such as a storage battery, dry cell battery, transformer, etc., the leads of which are connected to the electrodes 14 and I5 by means of the electrical conductors 23 and 24 through a 2-pole relay 2|. During the interval of time the electric current from the battery 22 is being impressed in a reversed direction from-the electrodes, a solenoid 25, actuated by a time element or clock 26, is energized, causing the battery circuit to close and the potentlometer circuit to open. The current flowing from the battery passes through the electrodes in a reverse direction to the normal flow and removes any protective film that has been formed on said electrodes. After a designated time interval, the solenoid 25 becomesde-energi'zed, the relay 2| takes up its normal position, cutting out the battery 22 from the circuit, and cutting in the recording potentiometer 2|l. Since the electrodes now have no protective film thereon, a high potential diflerence will be recorded on the potentiometer. If the solution is not corrosive to the alloy. a coating will form on the ;-electrodes and the potential dlfierence between the electrodes will consequently decrease until" the solenoid is again energized, impressing a counter electromotive force'through the electrodes. I

Should the solution I! become corrosiveat any time towards the electrodes, it will fail to replace.

- -said electrodes 'is not below a predetermined "value, a relay 2! becomes energized to actuate a suitable indicating or signal element 28, such as an alarm or flashing light. Operation of said alarm will direct an operators attention to the fact that the solution being tested is not of desired filmforming character and manual steps can then be taken to neutralize or otherwise correct the a rs s character of said solution and render it substanopen a suitable valve-controlled conduit leading from a suitable source of supply, such as a tank or vessel (also-not shown), wherein a neutraliz ing or-other compensating or corrective agent or fiuid is retained, whereby a requisite and sufficient quantity of such agent or fluid will be introduced into the container [0 to reduce or neutralize the corrosive character of-the solution present therein. By such type of automatic means, the liquor or slurry present in the .con- ,tainer can be maintained relatively constant qualitatively and in accordince with the adjustment of the automatic controlling relay switch.-

For periodically impressing a counter E. M. B. through the electrodes, a suitable timing element, such as a clock 2-6, connected to a relay (not shown) may be provided.- .Said; time clock may comprise any well known type of. operable electrical make which is adapted toactuate a relay for a predetermined interval of time. In our preferred embodiment, the counter E. M. F. from the battery is impressed across the electrodes for a period of about'30 seconds after the time clock cuts the battery from the circuit. It has been found that, for the particular corrosive materials being tested, a counter E. M. I". of seconds through the electrodes will eflect desired removal of the film formed thereon. Obviously, for any given corrosive material, it will be necessary to determine the time required to completecarbon, and the balance substantially all iron and cobalt, 15% tungsten and 30% chromium.

Other useful types or combinations of dissimilar skilled metals or alloys will be obvious to those in theart.

Further, the means disclosed for periodically removing the surface film from the electrodes are not to be construed as in limitation of our invention.

While in practice it has been found more convenient, preferable and efficient to em ploy electrical means for impressing a counter E. M. F. to the electrodes, as above described, other means may be employed, if desired. For

example, the surface film may be periodicallyremoved by mechanical means adapted to scrape the film from the electrodes or by placing in the solution in-which said electrodes are immersed a chemical which will be corrosive to the alloy or metal used for the electrodes. ations, however, it will be necessary and'desirable to have the electrodes situated on a bypass to the main iiow in order that the corrosive me-. dia will not come in contact with the equipment to be protected. Another means for periodically removing protective film from the-electrodes involves increasing the temperature ofthesolution being tested so that it will dissolve the surface film. While these methods all have certain advantages, it is nevertheless preferred to employ electrical means for automatically and periodically removing the surface film from the electrode as soon as such removal can be quickly and practically accomplished and while theprocess and all operating parts in conjunction therewith are maintained in statusuo and under substantially the same prevailing conditions of operation. 'Although, as indicated, the device is preferably automatically controlled, this is not an essential limitation to the operation of our invention since the film can be removed by manual control of the electrical energy. Since the automatic alarm, signalling 'or solution-corrective ly remove the protective film from the electrode, I

but such procedure will be merely a routine matter and readily understood by-those skilled in the art.

While the invention has been described in connection with certain preferred embodiments thereof, itis to beunderstood that the"same'-is not to be considered as limited thereto. Formstance, it will be readily'apparent that while;

particular types of electrodes have been em}, ployed herein, other types of dissimilar metallic electrodes may be used. In any given embodiment of the invention it is only essential that at least one of the plurality of electrodes employed shall be of such nature that it is capable of forming a. protective film against non-corrosive media,

and that it be of the same material as the equipment which is being protected. Conveniently,

the other or remaining electrodes may consist of any other dissimilar metal or alloy. For example,

electrodes having the following compositions equipment requires less operating attention and gives a positive in ation at all times of the condition of the solu on being tested, such automatic method constitutes our preferred form of the invention.

- Aswlll be evident, our invention many varied types of solutions, liquids or slurries, whether acid, alkaline or neutral. on alloys and metals. Thus, it will be found especially suitable for use in conjunction with the testing, control or regulation of relatively dilute or concentrated sulfuric, hydrochloric, nitric. phosphoric, etc. or other mineral or organic acid-containing solutions; of metallic salt solutions, including metalrides) etc., especially those of iron, zinc, aluminum, etc.; and of caustic solutions, such as those of potassium, sodium or barium hydroxide; as well as mixtures thereof.

As will be evident, novel means is providedby our invention for continuously and positively determining and/0r controlling the state -or condition of "any type of liquid media, and for particularly ascertaining whether such media is corrosive or non-corrosivein nature. Further, it provides mean for automatically controlling and regulating the quality or characteristic of a given liquid. or aqueous slurry to any desired condition or state. By its use, continuous information is had of the characteristics ofthe solution under test, whereby one may immediately ascertain at all times whether the solution in question will or In such op'erhas wide ap- ,plication in measuring the film-forming ability of 1 lie sulfates, halides (chlorides, bromides, fiuowill not attack or corrode metallic parts and equipment employed in commercial plant operations; From this standpoint alone, it has a high degree of practical value, especially as applied to processing costs and continuous operations. Another outstanding advantage resides in the'fact that periodicremoval of the protective film from the electrodes permits one to ascertain whether the protective film can or cannot be reformed by the solution under test. Thisrenders the device very much more sensitive as a corrosion recorder in that it permits determination as to the cxistonce or non-existence of incipient, as distinguished from advanced, corrosiveness. When the electrodes are employed without means for periodically removing such film, no measure of the filmforming ability of the liquid can be obtained. The particular liquid being tested does not need to destroy the protective film, but needs simply be incapable of reforminng such film. Since any injury to the protective film, either through corrosive media or by mechanical means, such as the formation of an adherent surface film on the steels, it is very important that immediate detection be had as to whether the surface film can be removed by the action of the liquor itself and thus become subject to rapid corrosion and deterioration. In accordance with our invention, we advantageously ascertain the presence of corrosive conditions through periodic sensitizing of the electrodes and before any appreciable attack occurs on the involved metals or parts. Thus, one may readily determine whether or not abnormal corrosion would occur if the protective surface film on the metals and alloys involved should be removed by any means, whether mechanical, electrical, or chemical. Thus, by the immediate ascertainment of incipient corrosiveness, the existence of subsequent abnormal corrosion can be readily forecast. We claim as our invention: Apparatus for indicating the film-forming ability of solutions and slurries on metallic materials, comprisingin combination, an electrical circuit, a source of electrical energy therefor, a pair of spacedly-disposed, interconnected electrodes in said circuit, composed of dissimilar metals and immersed in a solution to be tested, one of said electrodes conforming substantially to th composition of the metal material towards which the action of said solution or slurry is to be determined, a voltagemeasuring device also disposed in said circuit and responsive to the current fiowing therein, a second electrical circuit, a source of electrical energy therefor, means included in said second circuit for closing said first circuit and periodically impressing from the source of energy in said second circuit a counter E. M. F. in said first circuit to remove, at controlled time intervals, any protective film formed on said electrodes and periodically expose them, while in film-free condition, to the action of the solution being tested, and indicating means actuated by said voltage measuring device for indicating the failure of the solution or slurry to reform a protective film on said electrodes after said periodic counter E. M. F. L

has been impressed in said first circuit.

MAR/SELIO G. FONTANA. GORDON W. KIDDER. PHILIP B. KRAUS. 

